I can imagine getting a large amount of flaming for this idea, but wouldn't the logical extreme just be to basically define a container for a JS canvas with embeddable resources? In a more restricted form of course, to be sure that it will always render the same, and all compliant computers will have enough power to render it.
You could do things like 480p training videos with ultra-crisp text, and snow/fire/etc effects.
You'd probably have to prevent it from having network access or else you'd just be asking for the videos to rot over time, but you could give them an embedding API or even access to a few small bits of data, so you could have a YouTube video that changes with seasons and location.
If you were strict about the no network access thing you could give access to all sensors, since the data would never leave the device.
YouTube's already got some limited interactivity features, DVDs had them, why not all videos? It would mostly be a novelty, but you could also do really cool stuff like use Bluetooth beacons to skip around to certain parts for an interactive tour, although you might have to enforce downloading the whole thing before playing if you wanted 100% no privacy leaks.